1. Field of the Invention
This invention relates to the catalytic condensation reaction of alcohols, e.g., monoethanolamine, with amines, e.g., ethyleneamine, to form predominantly acyclic polyethyleneamines at high levels of selectivity and conversion, and to the particular catalyst used.
2. Prior Art
The reaction of ethylene dichloride (EDC) with aqueous ammonia, followed by neutralization of the amine hydrochlorides formed with caustic, represents the predominant manufacturing process for making ethyleneamines for the last sixty years. Separation of the ethyleneamines products from the brine solution by extraction, dehydration, or evaporative crystallization, followed by separation and purification of the amines, can be an energy- and maintenance-intensive, corrosive process. Further, the co-production of salt requires an environmentally responsible method of disposal. This process produces the whole range of commercially acceptable ethyleneamines products, from ethylenediamine (EDA) to DETA, TETA, TEPA, PEHA, and the higher polyethylenepolyamines. Product distribution is controlled mainly by varying the ammonia:EDC mole ratio and/or the product recycle in the reactor feed.
A second commercially practiced process involves the reaction of ammonia and ethylene oxide to make monoethanolamine, followed by reductive amination to produce mainly the lower molecular weight ethyleneamines, EDA, DETA, etc. This process tends to produce a much higher level of unwanted cyclic ethyleneamines in comparison to the EDC-based process.
Monoethanolamine (MEA) can also be reacted with ethyleneamines such as EDA to produce the higher ethyleneamines. This newer process technology produces a highly acyclic product composition in comparison to the EDC-based process. Phosphorus-containing, acidic catalysts for the reaction of EDA and MEA are well known. Representative of the prior art are U.S. Pat. Nos. 4,806,517; 4,588,842; 4,540,822; 2,824,073; and the references cited in them. The art is also extensively discussed in co-pending, co-assigned U.S. patent application Ser. Nos. 390,706, filed Aug. 8, 1989, now U.S. Pat. No. 5,202,492; 390,829, filed Aug. 8, 1989, now U.S. Pat. No. 5,202,489; and 742,731, filed Aug. 6, 1991, now U.S. Pat. No. 5,225,660 the disclosures of which are incorporated herein by reference. The '517 and '842 patents represent versions of phosphorus-containing catalysts in which the phosphorus compound is "thermally chemically" bonded to a "thermally activated," pelletized group IVb metal oxide (e.g., titania) by treating preferably pre-formed pellets with the liquid phosphorus compound in solution form, and thereafter subjecting the pellets to a thermal process. The catalysts so produced are deficient, however, in that under typical commercial reaction conditions, the amines formed tend to leach critical catalytic elements, such as phosphorus, from the catalyst composition, or otherwise adversely affect the structural integrity of the pellets. As stated in U.S. Pat. No. 4,806,517, "in an extreme instance, catalyst pellets having good initial crush strength and surface hardness will be reduced to fines very rapidly," and/or will lose their activity or selectivity, under reaction conditions. Significant loss of structural integrity results in plugging downstream of the reactor and catalyst leaching may cause reforming in the later stages of product refining. The affected catalysts typically tend to age rapidly.
Co-assigned U.S. Pat. No. 4,983,736, the disclosure of which is incorporated herein by reference, describes catalysts related to those of the present invention; however, the patented catalysts are disclosed as calcined at significantly lower temperatures.